Myocardial infarction and stroke due to atherosclerosis are the leading causes of death in the United States. It has become clear that increases in reactive oxygen species (ROS) represent a common pathogenic mechanism for atherosclerosis. A particularly important mechanism for ROS-mediated cardiovascular disease appears to be stimulation of pro-inflammatory events. In the proposed research we will investigate the role of a newly discovered class of ROS mediators that we term SOXF for Secreted Oxidative stress induced Factors. Published data suggest that cyclophilin A (CyPA), a member of the immunophilin family is an important SOXF that contributes to inflammation and atherosclerosis. We found that CyPA is secreted from vascular smooth muscle cells (VSMC) in response to ROS, and stimulates ERK1/2 and JAK/STAT pathways, increases DNA synthesis, and inhibits apoptosis in VSMC. In contrast to the effects in VSMC, CyPA stimulates endothelial apoptosis and increases expression of adhesion molecules including E-selectin and VCAM-1. Studies of the CyPA knockout mice (CyPA-/-) show that CyPA regulates T helper cell Th1 and Th2 responses. Our published data show that overexpression of CyPA enhances intima formation after vascular injury associated with enhanced inflammation, while CyPA deficiency has the opposite effects. Preliminary data show that CyPA deficiency decreases atherosclerosis in the apoE-/- mouse. Thus CyPA is a novel cytokine that mediates vascular inflammation and remodeling. We propose the following major hypothesis: CyPA, increased by oxidative stress, promotes vascular dysfunction and atherosclerosis by altering VSMC, endothelial and white blood cell function. To prove this hypothesis 4 aims are proposed. Aim 1: Characterize the signal transduction mechanisms by which CyPA modulates VSMC expression of pro- and anti-inflammatory mediators. Aim 2: Determine the role of CyPA in atherosclerosis development and progression by evaluating the effect of CyPA overexpression and deficiency on pathology of the apoE-/- mouse. Aim 3: Evaluate the role of bone marrow- derived cells in CyPA-mediated atherosclerosis. Aim 4: Show that ROS-mediated atherosclerosis is CyPA- dependent. These studies will provide new insight into the mechanisms by which ROS regulate vascular function and the specific role of CyPA in atherosclerosis.